Pulsed activation of trapped field magnets

ABSTRACT

A system for activating trapped field magnets in a superconducting material is disclosed. The system includes a superconducting material element and an electromagnet source disposed proximate the superconducting material element. The electromagnet source is configured to produce a magnetic field pulse sufficient to activate the superconducting material element. Furthermore, substantially all of a magnetic field generated by the magnetic field pulse is contained within an area that has smaller physical lateral dimensions than the superconducting material element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/710,847, filed Oct. 8, 2012 and entitled “Systems and Methods forPulsed Activation of Trapped Field Magnets;” and U.S. Provisional PatentApplication No. 61/824,903, filed May 17, 2013, entitled “Systems andMethods for Pulsed Activation of Trapped Field Magnets,” each of whichis incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to the activation ofsuperconducting trapped field magnets, and related methods and systems.

INTRODUCTION

The section headings used herein are for organizational purposes onlyand are not to be construed as limiting the subject matter described inany way.

Magnets have numerous applications, including, for example, the abilityto transfer electric energy into mechanical energy without much energyloss. Magnets are, therefore, an important component in varioustechnologies, including, for example, electric motors and generators.Permanent magnets (i.e., ferromagnetic materials that create their ownpersistent magnetic fields), however, can be significantly limited inthe magnitude of magnetic field which they can supply. Additionally,permanent magnets are composed of materials which are relatively rareand sometimes found in only limited geographical areas around the world.Accordingly, permanent magnets are expensive and sometimes costprohibitive for use in various applications.

Furthermore, conventional permanent magnet motors and generators havepower constraints, in which the amount of power that can be delivered islimited by the size and weight of the motor/generator which leads toconstraints on size and/or weight design parameters that can be undulylimiting. In general, shrinking the size of permanent magnets results ina decrease in power output due to the magnetic field strengthdecreasing. Power per unit volume (i.e., power density), therefore, canbe severely limited when ordinary permanent magnets are used in motors.Accordingly, there is a need for alternative materials with thepotential to produce persistent magnetic fields that are less expensive(i.e., contain less rare material) and are stronger (i.e., have largerfield magnitudes).

It has been discovered that a significant magnetic field can be“trapped” by a superconductor when it exhibits large flux pinningforces, which may result in a quasi-permanent magnetic material. Inother words, when a superconducting material is placed in a very highmagnetic field, the material may be activated to replicate the magneticfield, thereby producing its own persistent magnetic field. Inparticular, high temperature superconductors (HTSs) can be activated toform trapped field magnets (TFMs), and the resulting magnetic fieldshave been determined to be stronger than their permanent magnetcounterparts.

Although research has increased the understanding of HTSs and TFMs,improved TFM activation techniques can lead to greater, more reliableapplications. For example, current TFM activation generally has thefollowing limitations: 1) the TFMs need to be placed in a very highmagnetic field that is, for example, generated by a very large,expensive, and heavy magnet (e.g., permanent magnet or electromagnet);and 2) the TFMs need to remain very cold during the activation andoperation to hold the trapped magnetic field.

It may therefore be desirable to provide systems and methods for TFMactivation that not only provide practical and efficient TFM activation,but also provide robust TFMs that are fully activated. It may also bedesirable to provide systems and methods for TFM activation that rely onreduced electrical energy and heating.

SUMMARY

The present disclosure may solve one or more of the above-mentionedproblems and/or achieve one or more of the above-mentioned desirablefeatures. Other features and/or advantages may become apparent from thedescription which follows.

In accordance with an exemplary embodiment of the present disclosure, asystem for activating trapped field magnets includes a superconductingmaterial element and an electromagnet source disposed proximate thesuperconducting material element. The electromagnet source is configuredto produce a magnetic field pulse sufficient to activate thesuperconducting material element. Furthermore, substantially all of amagnetic field generated by the magnetic field pulse is contained withinan area that has smaller physical lateral dimensions than thesuperconducting material element.

In accordance with an additional exemplary embodiment of the presentdisclosure, a method for activating a trapped magnetic field in asuperconducting material includes generating at least one magnetic fieldpulse proximate a superconducting material element. Substantially all ofa magnetic field generated by the at least one magnetic field pulse iscontained within an area that has smaller physical lateral dimensionsthan the superconducting material element. Furthermore, the at least onemagnetic field pulse is sufficient to at least partially activate atrapped magnetic field in the superconducting material element.

Additional objects and advantages will be set forth in part in thedescription which follows, and in part will be obvious from thedescription, or may be learned by practice of the present teachings. Atleast some of the objects and advantages of the present disclosure maybe realized and attained by means of the elements and combinationsparticularly pointed out in the appended claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the present disclosure and claims, includingequivalents. It should be understood that the present disclosure andclaims, in their broadest sense, could be practiced without having oneor more features of these exemplary aspects and embodiments.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate some exemplary embodiments of thepresent disclosure and together with the description, serve to explaincertain principles. In the drawings,

FIG. 1 is a diagrammatic view of an exemplary embodiment of a system fortrapped field magnet (TFM) activation in accordance with the presentdisclosure;

FIG. 2 shows a graph illustrating the applied activating magnetic fieldB_(A) as a function of radial position r across an electromagnet (EM)used in the system of FIG. 1, when the current I_(EM) through the EM is10 amps;

FIG. 3 shows a graph illustrating the trapped magnetic field B_(T) as afunction of radial position r across the TFM in the system of FIG. 1,for an electromagnet current I_(EM) ranging from 0.3 amps to 1.5 amps;

FIG. 4 shows a graph illustrating the trapped magnetic field B_(T) as afunction of radial position r across the TFM in the system of FIG. 1,for an electromagnet current I_(EM) ranging from 1 amps to 6 amps;

FIG. 5 shows a graph illustrating the trapped magnetic field B_(T) as afunction of radial position r across the TFM in the system of FIG. 1,for an electromagnet current I_(EM) ranging from 4 amps to 40 amps;

FIG. 6 shows a graph illustrating the trapped magnetic field B_(T) as afunction of radial position r across the TFM in the system of FIG. 1achieved by both single pulses of electromagnet current 10amps≦I_(EM)≦430 amps and by field cooling to full activation in aconstant field;

FIG. 7 shows a graph illustrating the trapped magnetic field B_(T) as afunction of radial position r across another exemplary embodiment of aTFM in accordance with the present disclosure, achieved by single pulsesof electromagnet current I_(EM) of differing durations;

FIG. 8 shows a graph illustrating the creep rate B_(T)(t₁)/B_(T)(t₀) asa function of radial position r across the TFM in the system of FIG. 1,when the TFM is fully activated by a pulse of current I_(EM) of 430 ampsthrough the electromagnet;

FIG. 9 shows a graph illustrating the creep rate B_(T)(t₁)/B_(T)(t₀) asa function of radial position r across the TFM in the system of FIG. 1,when the TFM is partially activated at an electromagnet current I_(EM)of 254 amps;

FIG. 10 shows a graph illustrating the creep rate B_(T)(t₁)/B_(T)(t₀) asa function of radial position r across the TFM in the system of FIG. 1,when the TFM is partially activated at an electromagnet current I_(EM)of 20 amps;

FIG. 11 shows a graph illustrating the trapped magnetic field B_(T) as afunction of radial position r across a TFM in another exemplary systemfor TFM activation in accordance with the present disclosure;

FIG. 12 shows a graph illustrating the trapped magnetic field B_(T) as afunction of radial position r across the TFM in FIG. 11 for variousnumbers N of activation pulses at various electromagnet currents I_(EM);

FIGS. 13-16 show graphs illustrating trapped magnetic field B_(T) as afunction of radial position r across the TFM in FIG. 11 for variousnumbers N of activation pulses at various electromagnet currents I_(EM);

FIGS. 17-20 show graphs illustrating the trapped magnetic field B_(T) asa function of pulse number N for various radial positions r across theTFM in FIG. 11, at various electromagnet currents I_(EM);

FIG. 21 shows a graph illustrating the trapped magnetic field B_(T) as afunction of pulse number N for experimentally derived values ofB_(T)(r,N) fit by proposed phenomenological theory;

FIG. 22 shows a graph illustrating the trapped magnetic field B_(T) as afunction of radial position r across the TFM in FIG. 11 at variouselectromagnet currents I_(EM), and showing the decrease of the trappedmagnetic field B_(T) with increased current I_(EM) at large values of r;

FIG. 23 shows a graph illustrating both the measured and calculatedmagnetic field B* as a function of electromagnet current I_(EM) at aradial position r of 5.15 mm on the TFM; and

FIG. 24 shows a graph illustrating the improvement of trapped magneticfield B_(T) with decreasing temperature K for various types ofmanufactured TFMs.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Reference will now be made in detail to various exemplary embodiments ofthe present disclosure, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

Trapped field magnets (TFMs) have great potential to replaceconventional permanent magnets in numerous applications, and whenoperated at substantially low temperatures, exhibit stronger magneticfields than their permanent magnet counterparts. By way of example, aTFM motor can deliver the same amount of power as a conventionalpermanent magnet motor but with a significant reduction in size andweight. Although research has increased the understanding of TFMs, aneed remains for improved TFM activation techniques, which do notrequire, for example, exposing superconducting materials (i.e.,superconductors) to very large, constant magnetic fields, generated, forexample, by an expensive, large, and heavy magnet (i.e., permanentmagnet or electromagnet). Such conventional activation techniques thatuse, for example, high field electromagnets, are impractical foractivating and/or reactivating (e.g., when the TFM loses its magneticfield) a TFM residing within an application in use in a place other thana laboratory. That is in various applications it may be desirable toenable activation or reactivation onsite, or in situ, and it may beimpractical to do so if reliance is on, for example, a large, heavyelectromagnet.

An alternative to activation using very large constant magnetic fieldsis pulsed magnetic field activation, which can activate a TFM usingelectromagnets that are much smaller and lighter. However, magneticfield pulses, for example, may also generate heat that warms up theTFMs, making them lose all or part of their “trapped” field. Thus, aneed remains for improved activation techniques, including pulsedactivation techniques, for TFMs that not only provide practical andefficient TFM activation, but also provide TFMs that are fullyactivated. It may be desirable, therefore, to provide systems andmethods for TFM activation which use very short magnetic field pulses,which require less electrical energy and therefore smaller energysupplies, resulting in less heating of the TFM.

As used herein the terms “trapped field magnet,” “TFM,” or variationsthereof, refer to superconducting materials that have a significant“trapped” magnetic field, resulting in a quasi-permanent magneticmaterial. In other words, a TFM is a superconducting material that hasbeen activated to replicate a magnetic field to which it has beenexposed, thereby producing its own persistent magnetic field. Inparticular, high temperature superconductors (HTSs), which are materialsthat become superconductive above the boiling temperature of liquidnitrogen (77K), can be activated to form TFMs. In various embodiments ofthe present disclosure, for example, the superconducting material is aHTS material, such as, for example, yttrium barium copper oxide (YBCO).For example, an HTS composed of YBa₂Cu₃O_(7-δ), becomes superconductingat temperatures below about 93 K. Accordingly, TFMs in accordance withthe present disclosure that are made of YBCO can operate at temperaturesfrom about 93 K, down to a temperature of about absolute zero.Furthermore, as illustrated in FIG. 24, in general, the magnetic fieldheld by TFMs increases as the temperature decreases. FIG. 24, forexample, illustrates the dependence on temperature for two types ofmanufactured TFMs. The higher fields shown are for a radiation enhancedTFM, and the lower fields shown are for a chemically enhanced TFM. Thesingle data point at 50 K, 1 Tesla represents an attempt to create a TFMusing a HTS wire (a bismuth strontium calcium copper oxide (BiSCCO)wire) rather than a bulk TFM.

In various additional exemplary embodiments, the superconductingmaterial is a HTS material, such as, for example, RE₁Ba₂Cu₃O_(7-δ),where RE is chosen from Y, Nd, La, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu,Tb, or mixtures thereof. In various further embodiments, the HTS iscomposed of Bi₂Sr₂CaCu₂O_(x); (Bi,Pb)₂Sr₂CaCu₂O_(x); Bi₂Sr₂Ca₂Cu₃O_(x);(Bi,Pb)₂Sr₂Ca₂Cu₃O_(x); HgBa₂Ca₂Cu₃O_(δ); HgBa₂CaCu₂O₆; TlCaBa₂Cu₂O_(x);Tl₂Ca₂Ba₂Cu₃O_(x); or Nd_(1+x)Ba_(2-x)Cu₃O_(x). Those of ordinary skillin the art would understand, however, that the present disclosurecontemplates systems and methods for activating TFMs in varioussuperconducting materials, including, for example, various HTSmaterials, based on the application of the TFM, and is not intended tobe limited in any manner to the exemplary materials disclosed andclaimed herein. Furthermore, those of ordinary skill in the art wouldunderstand that the size of a TFM depends upon the application.Generally, larger TFMs are most desirable. TFMs in current applications,for example, range in size from about 1.5 cm to about 10 cm in diameter.Larger TFMs also can be used, but can pose difficulties in production bypresent activation techniques.

As used herein the terms “activate,” “activating,” “activated,”“activation,” and variations thereof, refer to the occurrence in which asuperconducting material is turned from an inert material into a magnetfrom, for example, exposure to a magnetic field. In other words, asuperconducting material may be activated to become a TFM, and a TFM mayalso be activated by reactivation to maintain and/or recover itsmagnetic field after having been first activated. A superconductingmaterial is fully activated when it has reached its full magnetizationpotential from an applied magnetic field and is considered saturated. Atthe present time TFMs are known to be able to trap fields of over 2Tesla at the temperature of liquid nitrogen at atmospheric pressure, and6 Tesla at lower pressures of liquid nitrogen. TFMs have been shown totrap up to 14 Tesla at a temperature of 48 K. A superconducting materialis said to be partially activated when it is magnetized, but has not yetreached its full magnetization potential. Furthermore, a fully activatedTFM will gradually lose some of its trapped field by a process known ascreep. Typically, creep causes a loss of about 3% to about 7% of thefield per decade of time. For example, a TFM having a trapped field of 2Tesla 1 day after activation may lose 0.08 Tesla (4%) by day 10 (afteractivation). Generally creep loss can be held to about 20% loss afterone year, with an additional 4% loss after 10 years. TFMs may also losemagnetic field strength and become only partially activated, forexample, by loss of cooling sufficient to maintain the magnetic field.

Various exemplary embodiments of the present disclosure contemplatesystems and methods for activating trapped field magnets (TFMs) in asuperconducting material, by exposing a superconducting material elementto a magnetic field pulse generated by an electromagnet source, such as,for example, an electromagnet. In various embodiments, for example, thesuperconducting material element, such as, for example, a hightemperature superconducting material (HTS) element is disposed proximatethe electromagnet source, such that, when a current is run through theelectromagnet source, the electromagnet source produces a magnetic fieldpulse that may activate the superconducting material element. In variousembodiments, for example, the electromagnet source may produce a singlemagnetic field pulse that fully activates the superconducting materialelement. In various additional embodiments, the electromagnetic sourcemay produce a plurality of magnetic field pulses to achieve a desiredlevel of partial activation.

Various embodiments of the present disclosure contemplate, for example,that a majority of a magnetic field generated by the magnetic fieldpulse is contained within an area with smaller physical lateraldimensions than the superconducting material element. For example,substantially all of a magnetic field generated by the magnetic fieldpulse may be contained within an area with smaller physical lateraldimensions than the superconducting material element. In other words, invarious exemplary embodiments, substantially the entire magnetic fieldgenerated by the magnetic field pulse is contained within an area withsmaller physical lateral dimensions than the superconducting elementexcept for small amounts of magnetic field that may be attributed toleakage. In various embodiments of the present disclosure, for example,the leakage is such that about 10% or less of the resulting magneticflux is outside of the area defined by the physical boundaries of thesuperconducting material element, for example about 5% or less of themagnetic flux is attributed to such leakage and is outside of the areadefined by the physical boundaries of the superconducting materialelement.

In this manner, the electromagnet source may be positioned such that themagnetic field pulse covers only a portion of the superconductingmaterial element (e.g., in a localized manner), such as, for example, aninterior portion of the superconducting material element. In variousembodiments, for example, the lateral dimensions (e.g., diameter) of themagnetic field source is smaller than the lateral dimensions (e.g.,diameter) of the superconducting material element and the magnetic fieldsource is positioned relative to the superconducting material elementsuch that the magnetic field pulse is directed within an outerperipheral boundary of the superconducting material element. While notwishing to be bound by a particular theory, it is believed that byapplying a magnetic field pulse in this relatively localized mannerwithin a boundary of the superconducting material element (i.e., suchthat the field works on the superconducting material element within anouter peripheral boundary of the superconducting field element), asuperconducting material may be more efficiently activated, whileapplying a magnetic field to the outside of a superconducting material(such that the field is at the periphery of and/or completely surroundsthe material) may require a larger pulse to achieve full activation. Inother words, it is believed that the applied field B_(A) should be afunction of the radial position r across the superconducting material,with B_(A) approaching zero at the periphery of the surface of thesuperconducting material.

FIG. 1 shows a diagrammatic view of an exemplary embodiment of a system100 for TFM activation in accordance with the present disclosure. Thesystem 100 comprises a superconducting material element 102 that isdisposed between two electromagnets 104 and 106. As shown in FIG. 1, invarious exemplary embodiments, the superconducting material has a diskshape (e.g., a puck shape) and is positioned between electromagnets 104and 106, such that electromagnet 104 is above the superconductingmaterial element 102 and electromagnet 106 is below the superconductingmaterial element 102 in the configuration of FIG. 1. In variousexemplary embodiments, the superconducting material element 102 is ahigh temperature superconducting material as described above, such as,for example, yttrium barium copper oxide. The electromagnets 104, 106can be wire-wound electromagnets with an iron (or other ferro-magnetic)core, comprising a split-field magnet. The electromagnets 104, 106 arewired such that the fields that they produce are in the same direction.

As shown in FIG. 1, in various embodiments of the present disclosure,the diameter of the superconducting disk 102 is greater than thediameter of each of the electromagnets 104 and 106, and theelectromagnets 104, 106 are positioned substantially centered on thesuperconducting disk 102. Accordingly, as described above, when anelectric current is run through the electromagnets 104, 106 (via, e.g.,a pulse generator 120 and/or a capacitor 130), the electromagnets 104,106 will each produce a magnetic field pulse that is large only in anarea with smaller physical lateral dimensions than the superconductingdisk 102. In other words, substantially all of the magnetic fieldproduced by each of the electromagnets 104, 106 will be within adiameter of the superconducting disk 102. In this manner, as describedbelow in more detail, in a prototype that was built and tested (seeEXAMPLE 1 below), in various exemplary embodiments, a single magneticfield pulse produced by the electromagnets 104, 106 can fully activatethe superconducting disk 102 to produce a fully activated TFM. Invarious embodiments, for example, a single magnetic field pulse canfully activate the superconducting disk 102. The pulses used haddurations ranging from about 10 ms to about 30 ms, but both shorter andlonger pulses are effective. In various embodiments, a short pulse isdesirable because it uses less energy, and causes less heating of theTFM.

As also described below in more detail, with regard to another prototypethat was built and tested (see EXAMPLE 2 below), in various additionalembodiments, a plurality of relatively short magnetic field pulsesproduced by electromagnets (e.g., similar to the electromagnets 104,106) can partially activate a superconducting disk (e.g., similar to thesuperconducting disk 102) to a predictable level of activation based,for example, on a governing principal disclosed herein.

In various embodiments of the present disclosure, the system 100 mayfurther include a mechanism to maintain the superconducting disk 102cold to permit the TFM activation. For example, system 100 can include acryostat 110 filled, for example, with liquid nitrogen at atmosphericpressure; and the superconducting material 102 and the electromagnets104, 106 may be disposed within the cryostat 110 to keep thesuperconducting material 102 cold so that the activated TFM does notlose its magnetic field. Lower temperatures of the coolant permit anygiven TFM to retain higher fields. Examples of this for two typicaltypes of TFMs are shown in FIG. 24. For example, liquid nitrogen may bekept in a closed container at pressures below atmospheric. In this case,temperatures below 77 K are achievable, and the field trapping abilityof the TFM increases significantly, as shown in FIG. 24

Those of ordinary skill in the art would understand that system 100 isexemplary only and intended to illustrate one exemplary embodiment of asystem for TFM activation in accordance with the present disclosure.Accordingly, those of ordinary skill in the art would understand thatthe superconducting disk 102 and electromagnets 104, 106 utilized withinthe system 100 may have various shapes, dimensions and/orconfigurations, and be formed from various materials, based, forexample, on a particular application and the desired trapped fieldstrength of the TFM. Additionally, although the system 100 utilizeselectromagnets 104, 106, systems in accordance with the presentdisclosure contemplate using any electromagnetic source known to thoseof ordinary skill in the art to produce the magnetic field pulses.Furthermore, although system 100 includes a cryostat 110 to cool thesuperconducting material 102, systems in accordance with the presentdisclosure may utilize any cooling means, device, structure, method,and/or technique known to those of ordinary skill in the art, including,but not limited to, an evaporated cold gas of a low temperature liquid.

Single Pulse Activation

Various design considerations and their impact on the operation of asystem for TFM activation, such as that depicted in FIG. 1, will now bedescribed for the activation of a superconducting material element witha single magnetic field pulse from electromagnets similar to the system100 described above.

Example 1

A prototype, having a set up in accordance with the exemplary system 100diagrammatically depicted in FIG. 1, was built and tested to confirm andstudy the activation capabilities of the disclosed exemplary system.Each electromagnet 104, 106 was a wire-wound split field electromagnetwith an iron core that was configured with 94 turns of 24-gauge coppermagnet wire. The outermost diameter of the electromagnet windings wasabout 18 mm, and the innermost diameter was about 12 mm (which was setby the ferromagnetic cores of soft iron). The superconducting disk 102was made of a bulk yttrium barium copper oxide (YBCO), and had a 20 mmdiameter with an axial length of about 8 mm. The pinning centers in thesuperconducting disk 102, as would be understood by those of ordinaryskill in the art, were made of Y₂BaCuO₅, and were elongated and refinedby platinum (Pt) doping.

The system 100 was first activated using the conventional field cooling(FC) technique, as would be understood by those of ordinary skill in theart. When fully activated in air (no iron present) the maximum trappedfield (B_(T)) at 77 K was 4,400 gauss (G) at 0.8 mm from the surface ofthe superconducting disk 102. When fully activated by field cooling withthe coils and iron cores attached, the maximum trapped field (B_(T)) at77 K was 6600 G at 0.7 mm from the outer lateral surface of thesuperconducting disk 102. The measured values of the trapped fields(B_(T)) theoretically extrapolated to the surface of the superconductingdisk 102, were 35% higher. For example, the superconducting disk had asurface field of 5900 G, in air. Further theoretical extrapolation tothe mid a, b plane of the superconducting disk 102 yielded a field anadditional 60% higher at 9700 G in air. The presence of the iron coresin the electromagnets 104, 106 provided a higher applied field (B_(A))for a given coil current (I_(EM)) by lowering the reluctance of pathsfor the magnetic flux. In the same manner, the iron cores were found topermit a higher value of maximum trapped field (B_(T, Max)) for a givenvalue of the critical current (J_(C)) of the HTS used.

As shown in FIG. 1, in various embodiments, a Hall probe array 108 maybe disposed between the superconducting disk 102 and the electromagnet106 to collect data from the system 100. In the prototype tested inExample 1, the Hall probe array 108 was disposed in a 1.4 mm gap betweenthe superconducting disk 102 and the electromagnet 106, such that theprobe array 108 was sandwiched about 0.7 mm from the surfaces of thesuperconducting disk and the iron core of the electromagnet 106.Individual Hall probes (not shown) were spaced about every 1.15 mm tocover the radius of the superconducting disk 102 from 1.7 mm to 8.6 mmof the 10 mm radius of the superconducting disk 102. Data from the Hallprobe readouts were logged on a data logger (i.e., PC) 112, using anAREPOC™ interface.

Two pulse types were available for activation of the superconductingdisk 102. The first type was produced by a pulse generator, labeled 120in FIG. 1 that drove a fast rise time current supply, labeled 122 inFIG. 1, having a 20 ms rise time, a 100 ms flat top, and a 20 ms falltime. It was found, however, that with this pulse type activation,magnetic field pulses above 40 amps (A) heated the coils of theelectromagnets 104, 106. Accordingly, a second type of pulse was used togenerate higher magnetic field pulses (i.e., above 40 amps) using acapacitive discharge, from a 0.125 Farad (F) capacitor, labeled 130 inFIG. 1, rated at 100 volts (V). Circuit resistance was 0.236Ω (±8%) andinductance was negligible. Thus, the RC time of the capacitive dischargepulses was about 29.5 ms.

An oscilloscope, labeled 114 in FIG. 1, was used to read voltages acrossa low resistance shunt, labeled 116 in FIG. 1, for calibration studiesand current measurement. FIG. 2, for example, shows a measurement of thefield produced by the electromagnets 104, 106, or the applied field(B_(A)), when the current (I_(EM)) through the electromagnets 104, 106was 10 A. To avoid repetitive descriptions, the approximation is usedthat a current of 10 A produces a field of about 1500 G, i.e., thatB_(A) is approximately 150 G/Amp. This approximation may be amended inthe region of core saturation, as would be understood by those ofordinary skill in the art.

As shown in FIG. 2, the concentration of the magnetic field at theperiphery of the electromagnet's iron core resulted in a small peak inB_(A) at a radius (r) of the disk 102 of about 5.5 mm. Accordingly, thisfield distribution met the objective that much of the field distributionwas inside a ring of the superconducting disk 102 (i.e., such that thefield worked on the material within the outer peripheral boundaries ofthe disk 102). The applied field B_(A) was, therefore, a function of r,and was near zero at the periphery of the superconducting disk 102.

With reference to FIGS. 3-6, the trapped magnetic field B_(T) wasstudied as the applied field B_(A) was varied during the prototypetesting. Using the probe array 108, data was taken on the trapped field(B_(T)) as a function of radial position r across the superconductingdisk 102, for varying magnitudes of electromagnet current (I_(EM)).Using the prototype, testing was conducted wherein the current wasvaried from 0.3 A to 430 A. At I_(EM)≦40 A, data was taken using currentpulses shaped by the pulse generator 120, and at I_(EM)>40 data wastaken using current pulses generated by the capacitor 130.

FIG. 3 shows results for the trapped magnetic field (B_(T)) as afunction of radial position r across the superconducting disk 102, withcoil current as a parameter, for an electromagnet current (I_(EM))ranging from about 0.3 A to about 1.5 A. As illustrated in FIG. 3, B_(T)became of measureable magnitude in the range 5≦r≦10 mm for I_(EM)≧0.3 A(B_(A) ˜45 G). Furthermore, B_(T) was largest at the largest values of rand dropped rapidly as r decreased. B_(T) remained near zero for r<5 mm.It is also noteworthy that 45 G was far below the first critical fieldB_(C1), which scientific literature reports to be 200 G-300 G, forfields parallel to the c axis of the disk 102. (see e.g., R. Liang, P.Dosanjh, D. A. Bonn, and W. N. Hardy, and A. J. Berlinsky, “Lowercritical fields in an ellipsoid-shaped YBCO single crystal,” Phys. Rev.B 50, pp. 4212-4215 (1994)). Thus, in this region the applied field(B_(A)) amplitude was below the critical field B_(C1).

FIG. 4 shows results for the trapped magnetic field (B_(T)) as afunction of radial position r across the superconducting disk 102, foran electromagnet current (I_(EM)) ranging from 1 A to 6 A (150≦B_(A)≦900G). As illustrated in FIG. 4, a peak in B_(T) developed at 6 mm<r<9 mm.This peak was attributable to the peak in the structure of B_(A)(r) (seeFIG. 2). This peak first appeared at r>5.5 mm due to the slope in B_(T)at large r. But as I_(EM) increases, it would be seen to gradually movetoward about 5.5 mm. Thus, as I_(EM) increased, it reached a point atwhich the peripheral values of B_(T) are decreased as B_(A) increases.

FIG. 5 shows results for the trapped magnetic field (B_(T)) as afunction of radial position r across the superconducting disk 102, foran electromagnet current (I_(EM)) ranging from 4 A to 40 A. Asillustrated in FIG. 5, in this region of activation, the peak at theperiphery of the superconducting disk 102 grows smaller, the second peak(attributed to B_(A)(r)) migrates toward r ˜5.5 mm, and a third peakdevelops. This third peak may be interpreted as the peak predicted byBean's critical state model for zero field cooled (ZFC) activation. Theobserved slope (dB_(T)/dr) is proportional to the current density. Theslope of the high r side of the third peak increased as I_(EM) increasedand, in FIG. 4, has a maximum slope of dB_(T)/dr=130 G/mm. When thesuperconducting disk 102 was in its fully activated state (see FIG. 6)dB_(T)/dr=900 G/mm. The Bean model, for ZFC activation of an HTSmaterial, for example, predicts that the slope, dB/dr, in this region isconstant, and always equal to the slope of the fully activated HTSmaterial. (see e.g., C. P. Bean, “Magnetization of High-FieldSuperconductors,” Rev. Mod. Phys. 36, pp. 31-39 (1964)). Thus, withreference to the data depicted in FIGS. 4 and 5, the HTS current (J) isonly equal to J_(C) when activation is complete. Prior to that J variesthrough a range from very low values up to J_(C). This may becomplicated by the magnetic field gradually penetrating thesuperconducting material's layers as I_(EM) increases.

Various embodiments of the present disclosure also contemplateactivation of the superconducting disk 102 via a capacitive dischargepulse. As above, during the experiments, with pulse generator pulses of20 ms rise time, 100 ms flat top, and 20 ms fall time, theelectromagnets 104, 106 showed signs of heating if I_(EM)≧40 A.Accordingly, to avoid heating effects, shorter capacitive-dischargepulse durations may be used. The effects of varying pulse duration werestudied and found to be small, but significant. Comparison of B_(T)(r)resulting from capacitive magnetic field pulses against magnetic fieldpulsed from a pulse generator was accordingly also considered.

In further testing, capacitive discharge pulses (e.g., from capacitor130) having a rise time of about 1 ms and an exponential decay time (RC)of 29.5 ms were applied to the electromagnets 104 and 106, and data wastaken (via the probe 108) as the current of the pulses was varied from110 A to 430 A. FIG. 6 shows results for the trapped magnetic field(B_(T)) as a function of radial position r across the superconductingdisk 102 achieved by the capacitive discharge pulses of electromagnetcurrent (I_(EM)). As illustrated in FIG. 6, at I_(EM)=110 A, there wasstill a hint of the double peak structure seen at 40 A. As I_(EM)increased, however, B_(T)(r) for the capacitive pulses approached alimit at I_(EM)=430 A, which indicated that the superconducting disk 102was fully activated (and had reached saturation).

To verify that the superconducting disk 102 was fully activated, theprototype (with the coils and iron cores in place) was inserted into alarge electromagnet (a “C” magnet) at a field of 18,000 G, and thesuperconducting disk 102 was activated by the conventional field cooling(FC) method. FIG. 6 also shows the results for the trapped magneticfield (B_(T)) as a function of radial position r across thesuperconducting disk 102 achieved by this method, which is representedby the C-Mag data points shown on the plot. As illustrated by FIG. 6,there was a negligible difference between B_(T)(r) achieved by a singleRC pulse of 430 A (˜2.9 T) and that obtained by the FC method.

It was found that, because the iron cores of the electromagnets 104, 106became saturated in the neighborhood of 1 to 2 T, the field no longerscaled with I_(EM). Although the μ(H) values for the iron used for thecores were not determined, it was found that the applied field (B_(A))was not strongly dependent on this. It is believed that the lack ofsensitivity to μ(H) in the iron is due in part to the fact that theaverage μ, including the ferromagnetic and non-ferromagnetic portions ofthe magnetic circuit, was only about μ=3. If one considers μ(H) for twowidely different materials, soft iron or 1010 steel, in the case of softiron one can estimate that 430 A corresponds to 3.1 T, while in the caseof 1010 steel it corresponds to 2.7 T. Thus, the capacitive dischargepulse height required to completely activate the superconducting disk102 of the prototype (with iron attached) was concluded to beB_(A)≈2.9±0.2 T.

The results thus demonstrated that the superconducting disk 102 of theprototype was fully activated to B_(T,MAX)≈0.66 T (6600 G), at Z=0.7 mm,by a single capacitive discharge pulse of 430 A (˜2.9 T), with RC decaytime of 29.5 ms. Full TFM activation was obtained atB_(A)/B_(T,MAX)≈4.4. For B_(T), at the TFM surface B_(A)/B_(T,MAX)^(s)≈3.3. Accordingly, full activation was obtained by a single pulse ofapplied field B_(A) about 3.3 times the maximum trapped field(B_(T,MAX)) on the surface of the superconducting material element.

Various embodiments further contemplate using a single capacitivedischarge pulse with a shorter length, such as, for example, an RC decaytime of 10 ms. FIG. 7, for example, shows data from another prototypetesting of a system similar to the system 100 of FIG. 1, which used aTFM having a higher trapped field. FIG. 7 demonstrates the trappedmagnetic field (B_(T)) as a function of radial position r across asuperconducting disk achieved by a single 30 ms pulse of electromagnetcurrent I_(EM) and by a single 10 ms pulse of electromagnet current(I_(EM)). The 30 ms pulse was produced with a capacitor of 0.125 F andthe 10 ms pulse was produced with a capacitor of 0.025 F, and bothpulses were adjusted to supply 200 A to the electromagnet coils toproduce the same magnetic pulse height. As illustrated in FIG. 7, withinthe errors of setting up a change in the prototype system to obtainequal currents, the two results were the same with each pulse producingthe same amount of partial activation. According, it was determined thata significant change in pulse length (e.g., by a factor of 3) does notsignificantly change the resulting trapped magnetic field (B_(T)).

As shown in FIGS. 8-10, in further testing, creep rates were measured asa function of radial position r across the superconducting disk 102 forseveral values of the activation pulse height. Creep measurementsstarted 20 s following the applied magnetic field pulse.

As would be understood by those of ordinary skill in the art, the lossof B_(T), following activation, is very nearly a constant decrease perdecade of time. For t₂>t₁,

$\begin{matrix}{{{B_{T}\left( t_{2} \right)} = {{B_{t}\left( t_{1} \right)}\left\lfloor {1 - {b\; \log \frac{t_{2}}{t_{1}}}} \right\rfloor}},} & (1)\end{matrix}$

where creep (b) (which is the % decrease in field per decade of time) isalmost time independent. In the following, creep is quantified by notingthe value of b.

FIG. 8 shows the creep rate B_(T)(t₁)/B_(T)(t₀) as a function of radialposition r across the superconducting disk 102, when the disk 102 hasbeen fully activated by a pulse of electromagnet current (I_(EM)) of 430A. As illustrated in FIG. 8, the creep (b) at all values of r are verynearly the same for this case. The value of b≈7% per decade of time wasobserved.

FIG. 9 shows the creep rate B_(T)(t₁)/B_(T)(t₀) as a function of radialposition r across the superconducting disk 102, when the disk 102 hasbeen partially activated by a pulse of electromagnet current (I_(EM)) of254 A. As illustrated in FIG. 9, at this partial activation, the creep(b) is a function of r, and the value of b varies monotonically with rfrom b<4% at r=1.7 mm to b>7% at r=8.6 mm.

FIG. 10 shows the creep rate B_(T)(t₁)/B_(T)(t₀) as a function of radialposition r across the superconducting disk 102, when the disk 102 hasbeen partially activated by a pulse of electromagnet current (I_(EM)) of20 A (B_(A) ≈3000 G). As illustrated in FIG. 10, at this partialactivation b not only varied with r, but the variation was no longermonotonic. At r=1.7 mm, b was essentially zero; b then increased to amaximum of ˜5% at r=5.15 mm, and then decreased for higher values of r.

Accordingly, the above experimental testing confirmed that when thefield applied to activate the superconducting disk was localized, suchthat substantially the entire field was limited in radius to a valuesmaller than the radius of the superconducting disk, full activation canbe obtained by a single pulse of applied field. Furthermore, for partialactivation of the superconducting disk, creep (b) was found to vary withradial position r across the superconducting disk. As full activationwas approached, however, the disparate values of b coalesced to a singlevalue. For, example, in accordance with the embodiment tested, b wasabout 7% at full activation. Various embodiments of the presentdisclosure may, therefore, provide systems and methods for TFMactivation that provide for activating superconducting material elementsto become fully activated TFMs or activations that that are onlypartial, and are minimally affected by creep.

Multiple Pulse Activation

Experiments were also conducted to determine the effects of multi-pulseactivation, for example, to compare the activation capabilities of aseries of very short magnetic field pulses with the activationcapabilities of a single magnetic field pulse. The results andconclusions of these experiments are described below.

Example 2

Following the above study of single pulse activation and varyingmagnetic field pulse height, another prototype similar to that used inEXAMPLE 1 was built to the same specifications as described above,however, allowable errors could and did change between the two prototypesystems. For example, in the second prototype system of EXAMPLE 2, theHall probe array 108 was positioned 0.8 mm from the surface of thesuperconducting disk 102, rather than 0.7 mm as in the aboveexperiments. This change, albeit small, nevertheless reduced Hall probetrapped field readings by about 10%. Thus, the peak trapped field(B_(T)) readings (see FIG. 11) for the second prototype system ofEXAMPLE 2 were lower than in the above experiments by about 10%. Asshown in FIG. 3, in the prototype system of EXAMPLE 2, full activationwas read as 6007 G (compared to 6600 G for the prototype system ofEXAMPLE 1).

As above, two pulse types were used for activation of thesuperconducting disk 102. A pulse generator that drove a fast rise timecurrent supply having a 20 ms rise time, a 100 ms flat top, and a 20 msfall time was used for magnetic field pulses less than or equal to 40 A;and a capacitive discharge, from a 0.125 F capacitor rated at 100 V, wasused for magnetic field pulses greater than 40 A. As above, the RC timeof the capacitive discharge pulses was about 29.5 ms.

It has been determined that an increase in trapped field (B_(T)) dependson the radial position, r, at which the field on the superconductingmaterial element is measured, the magnitude of the pulse of appliedfield (as measured by the electromagnet current, I_(EM)), and the numberof pulses, N (B_(T)=B_(T)(r, I_(EM), N)).

FIGS. 12-16 show results measured for the trapped magnetic field (B_(T))as a function of radial position r across the superconducting disk 102of the EXAMPLE 2 prototype, following N multiple activation pulses at anincreasing range of electromagnetic currents (I_(EM)). FIGS. 12-16,therefore, show B_(T) vs. r, with N as a parameter at fixed values ofI_(EM). FIG. 12 compares results for B_(T)(r) for a single pulse (N=1)with multiple pulses (N=10) at I_(EM)=6 A and I_(EM)=10 A. FIGS. 13-16show results for B_(T)(r) for various numbers N of activation pulses atrespective electromagnet currents of I_(EM)=20 A, 40 A, 110 A, and 228A.

In order to analyze the dependence of the trapped magnetic field (B_(T))on the number of pulses N applied, graphs of B_(T) vs. N, with r as aparameter, can be generated. Accordingly, FIGS. 17-20 illustrate thisfunctional relationship (B_(T) as a function of pulse number N)normalized to the value of B_(T)(r, N=1), which isolate the radialposition r as a parameter at fixed values of I_(EM) (i.e., I_(EM)=20 A,110 A, 170, and 280). The data for each of the FIGS. 17-20 is shown on asemi-log graph in order to emphasize that the data follows the form:

$\begin{matrix}{\frac{B_{T}\left( {r,N} \right)}{B_{T}\left( {r,{N = 1}} \right)} = {1 + {k\mspace{14mu} \log \mspace{14mu} N}}} & (2)\end{matrix}$

where k is independent of N, but dependent upon r and I_(EM). The valuesof k that were used are presented in TABLE 1 below:

TABLE 1 Values of k(r, l_(EM)) l_(EM)(A) r(mm) 10 20 50 65 92 110 170228 280 1.70 0.372 0.339 0.365 0.356 0.610 0.842 0.873 1.280 1.322 2.850.685 0.392 0.386 0.364 0.532 0.627 0.739 1.115 1.246 4.00 0.777 0.3980.244 0.233 0.317 0.400 0.574 1.000 1.195 5.15 0.573 0.367 0.246 0.3610.341 0.268 0.529 1.004 1.245 6.30 0.434 0.022 0.335 0.377 0.439 0.3480.575 1.066 1.382 7.45 0.252 0.488 0.347 0.364 0.464 0.415 0.591 1.3671.906 8.60 0.751 0.646 0.394 0.469 0.536 0.490 0.655 0.441 1.752

Accordingly, as N increases, the increment in trapped field decreases asd(logN)=(k/N)dN. As the number of pulses increases, the increase inB_(T)(r, N) for the Nth pulse varies as k/N:

$\begin{matrix}{{\frac{\Delta \left( {B_{T}\left\lbrack {r,N} \right\rbrack} \right)}{B_{T}\left\lbrack {r,{N = 1}} \right\rbrack} = \left( \frac{k}{N} \right)},} & (3)\end{matrix}$

In other words, the effectiveness of the Nth pulse to cause an increasein B_(T) decreases as 1/N.

As illustrated in FIGS. 17-20, the data in the present experimentconfirmed the log N behavior over a wide range of I_(EM) values.Deviations, however, were also discovered from the log N behavior. Onesuch deviation is illustrated, for example, in FIG. 18, for data atI_(EM)=110 A. As shown in FIG. 18, the data for the lowest values of rdeviated systematically from log N behavior, with deviations ofapproximately 15%. In FIG. 19, for data at I_(EM)=170 A, the deviationsappeared somewhat smaller.

In addition to these small deviations, the log N behavior also wasdetermined to be more substantially limited at a high value of thetrapped field (B_(T)). In light of log N in equation (2) growing withoutlimit as N→∞, equation (2) would indicate that B_(T)(r) grows to aninfinite trapped field, as N→∞. However, it has been determined thatB_(T,MAX) is physically limited to finite values by finite J_(C). Thus,a modification to equation (2) was sought, which limits B_(T)(r, N→∞) tosome finite value smaller than or equal to the value of B_(T,MAX)(r) setby J_(C).

In order to observe the limiting behavior, studies were focused on thehigh-pulse activation data at, e.g., I_(EM)=280 A (see FIG. 20). Asillustrated in FIG. 20, as expected, the experimental increases ofB_(T)(r, N), which had been proportional to log N, leveled off andbecame saturated at higher values of N.

To find a phenomenological equation to accommodate the saturation ofB_(T)(r, N), equation (3) was modified with a multiplicative correctionterm in which the increase in trapped field, ΔB_(T)(r, N), on the Nthpulse approaches zero, as N→∞, and the trapped field, B_(T)(r, N)approaches whatever its limiting value may be at very large N. Thislimiting value was designated as B*(r, I_(EM)).

Accordingly, a simple saturation term was considered:

$\left\lbrack {1 - \frac{B_{T}\left( {r,I_{EM},{N - 1},} \right)}{B^{*}\left( {r,I_{EM}} \right)}} \right\rbrack$

which made the increment in trapped field on the Nth pulse:

$\begin{matrix}{{\Delta \; {B_{T}\left( {r,N} \right)}} = {\frac{{B\left( {r,{N = 1}} \right)}k}{N}\left\lbrack {1 - \frac{B_{T}\left( {r,I_{EM},{N - 1}} \right)}{B_{T}^{*}\left( {r,I_{EM}} \right)}} \right\rbrack}} & (4)\end{matrix}$

The trapped field, following the N^(th) pulse then be determined by:

$\begin{matrix}{{B_{T}\left( {r,N} \right)} = {{B_{T}\left( {r,{N = 1}} \right)} \times \left( {1 + {\sum\limits_{2}^{N}\; {\frac{k}{N}\left\lbrack {1 - \frac{B_{T}\left( {r,I_{EM},{N - 1}} \right)}{B^{*}\left( {r,I_{EM}} \right)}} \right\rbrack}}} \right)}} & (5)\end{matrix}$

Equation (5) was tested to see if the experimental values of B_(T)(r, N)fit the data, for some choice of B*. For example, if the data fit theequation, for some value of B*, equation (5) could be further used toquantify B*(r, I_(EM)) and potentially identify the physical nature ofthe limiting field. In FIG. 21, for example, the curves joining theexperimental points resulted from applying equation (5) and finding abest value of B*(r, I_(EM)). The best values of B*(r), at the givenvalue of I_(EM), are shown in FIG. 21 for each measured value of r.Accordingly, equation (5) provided a very good fit to the experimentaldata, and it was concluded that the modification of the log N lawpresented in equation (5) was an applicable phenomenological law thatrepresents the multi-pulse data. The value of trapped field followingthe first pulse, B_(T)(r, N=1), however, is not described by equation(5). The values of trapped field following the first pulse can insteadbe directly obtained from the plots of the trapped field achieved by thefirst pulse (see FIGS. 12-16).

The values of B*(r) also were found to be very sensitive to any type oferror in the data, or any anomaly due to varying physical mechanisms inthe activation process. Both error types exist in the data reportedhere. It was noted that there were two regions within the values of (r,I_(EM)) in which the fits of equation (5) to the data points weresignificantly different than could be accounted for by the knownexperimental errors in measuring values of B_(T)(r, N, I_(EM)). One ofthese regions was at the lowest values of r, and the other was at thehighest values of r. It was determined that the first problematic region(at the lowest values of r) was due to a defect (a chip) in thesuperconducting disk 102 in the region 0≦r≦2, and that the secondproblematic region (at the highest values of r) was due to the anomalousactivation behavior exhibited at high r proximate the outer periphery ofthe superconducting disk 102 shown, for example, in FIG. 22.

The errors (at low r and high r) were sufficiently large enough toimpact the ability to make general conclusions concerning B* in theseregions. However, the data at r=5.15 mm, for most values of I_(EM) wasbetween these error prone regions, and permitted a conclusion to bedrawn concerning the physical nature of B*(r). The analysis of B*(r=5.15mm, I_(EM)) is summarized in FIG. 23. If B*(r=5.15 mm, I_(EM)) wereequivalent to the maximum obtainable field, B_(T,MAX)(r=5.15 mm), thedata would all fall at the same value of trapped field, independent ofI_(EM). Instead it is shown that B* is essentially zero at low I_(EM),and rises until I_(EM) is approximately 100 A (B_(A) is approximately15,000 G), after which it is approximately flat. The behavior,therefore, appears to be that of a zero field cool (ZFC) TFM type ofactivation in various constant and uniform applied fields.

In order to compare the values of B* to ZFC activation in a constantmagnetic field, finite element calculations were done for activations ofthe superconducting disk (of the EXAMPLE 2 prototype) in constantmagnetic fields, in the same excitation geometry as used in theexperiments. The values of constant field in these calculations weredetermined for each value of I_(EM). The results of these calculationsare shown by the plotted points in FIG. 23.

It was therefore concluded from the data and calculations that B*(r,I_(EM)) for pulsed activation is the maximum value of B_(T)(r, I_(EM))reached by a ZFC activation in a constant field of the same magnitude asthe pulsed field.

Accordingly, the above experiments determined that the trapped fieldincrement, due to the Nth magnetic field pulse, increases at a rate nolarger than 1/N, and that the rate of increase approaches zero when thetrapped field approaches the value obtained in ZFC activation by aconstant field of the same magnitude as the pulsed field. In otherwords, it was determined that sequential small magnetic field pulses(i.e., multiple activation pulses) were not an improvement over a singlelarger magnetic field pulse when attempting to fully activate a TFM. Forexample, if the first pulse does not fully activate the TFM, no amountof additional pulses will eventually accomplish full activation(although it may be possible to slightly increase the amount of trappedfield via multiple pulses short of reaching full activation).Furthermore, the phenomenological law which was developed in equation(5) governs the use of multiple pulses in a row, such that once twopulses (N=2) are used, one can predict the state of the TFM at anynumber N of pulses, thus providing the ability to predict the amount ofpartial activation after N pulses using equation (5).

An exemplary method for activating trapped magnetic field in asuperconducting material in accordance with an exemplary embodiment ofthe present disclosure is set forth in the following description withreference to the embodiment of FIG. 1. At least one magnetic field pulsemay be generated proximate a superconducting material element 102, whichcan, for example, be in the form of a solid superconducting disk orother configuration. In accordance with various embodiments of thepresent disclosure, a majority, e.g., substantially all, of a magneticfield that is generated by the at least one magnetic field pulse iscontained within an area that has smaller physical lateral dimensionsthan the superconducting material element 102. With reference to thedisk shaped embodiment of FIG. 1, for example, substantially all of themagnetic field is within a diameter smaller than a diameter of thesuperconducting disk 102. Thus, as described in detail above, the atleast one pulsed magnetic field is applied in a localized manner to aportion of the superconducting material element 102 the majority ofwhich is within the outer peripheral boundaries of the element 102. Inthis manner, the at least one magnetic field pulse is sufficient to atleast partially activate a trapped magnetic field in the superconductingmaterial element 102. In various exemplary embodiments, the at least onemagnetic field pulse is sufficient to fully activate the superconductingmaterial element 102 to a TFM.

In various exemplary embodiments, the superconducting material element102 may be disposed proximate an electromagnet source, such as, forexample, electromagnets 104, 106 (see FIG. 1), and the at least onemagnetic field pulse may be generated by the electromagnets 104, 106. Invarious embodiments, for example, the electromagnets 104, 106 maygenerate the at least one magnetic field pulse when an electric current(via e.g., a pulse generator 120 and/or a capacitor 130) is run throughthe electromagnets 104, 106.

In various exemplary embodiments, the electromagnets 104, 106 maygenerate a single magnetic field pulse, such as, for example, a singlemagnetic field pulse having a duration ranging from about 10 ms to about30 ms or longer. In various additional embodiments, the electromagnets104, 106 may generate a plurality of magnetic field pulses. In variousembodiments, for example, a number of magnetic field pulses generatedmay be selected based on a predicted amount of trapped magnetic field inthe superconducting material element 102, such as, for example, based onthe above equation (5).

As above, to keep the superconducting material element 102 cold so thatthe activated TFM does not lose its magnetic field, in variousembodiments, the superconducting material element 102 may also be cooledto maintain a temperature sufficient to maintain activation of thesuperconducting material element 102. In various embodiments, forexample, the superconducting material element 102 may be cooled by acryostat 110, which houses the superconducting material element 102 andthe electromagnets 104, 106, or by an enclosed volume of liquid nitrogenmaintained at below atmospheric pressure in order to reduce itstemperature.

Systems and methods for activating TFMs as disclosed herein havenumerous applications, including, for example, magnetic drive devices,such as, for example, magnetic motors, which in accordance with thepresent disclosure may be used in various industrial applications withwhich those of ordinary skill in the art are familiar. Such applicationsmay include, but are not limited to, hydraulic pumps, drills, andvarious additional rotating drive shafts, such as, for example, atop-drive mechanism used in the oil and gas industry. Magnetic motorsutilizing the TFM systems described herein may, for example, providecompact yet robust magnetic motors, which provide for onboard, or insitu, activation and/or reactivation of TFMs. Such systems may, forexample, be particularly beneficial in operating industrial rotaryequipment located in challenging and/or inaccessible environments, suchas, for example, on oil rigs, in which size constraints often limit thepower output of conventional permanent magnet motors.

Although only a few exemplary embodiments have been described in detailabove, those skilled in the art will readily appreciate that manymodifications are possible in the example embodiments without materiallydeparting from this disclosure. Accordingly, all such modifications areintended to be included within the scope of this disclosure as definedin the following claims.

It is to be understood that the various embodiments shown and describedherein are to be taken as exemplary. Elements and materials, andarrangements of those elements and materials, may be substituted forthose illustrated and described herein, and portions may be reversed,all as would be apparent to one skilled in the art after having thebenefit of the description herein. Changes may be made in the elementsdescribed herein without departing from the spirit and scope of thepresent disclosure and following claims, including their equivalents.

Those having ordinary skill in the art will recognize that variousmodifications may be made to the configuration and methodology of theexemplary embodiments disclosed herein without departing from the scopeof the present teachings. By way of example only, the cross-sectionalshapes and relative sizes of the superconducting material andelectromagnets may be modified and a variety of cross-sectionalconfigurations may be utilized, including, for example, circular or ovalcross-sectional shapes.

Those having ordinary skill in the art also will appreciate that variousfeatures disclosed with respect to one exemplary embodiment herein maybe used in combination with other exemplary embodiments with appropriatemodifications, even if such combinations are not explicitly disclosedherein.

For the purposes of this specification and appended claims, unlessotherwise indicated, all numbers expressing quantities, percentages orproportions, and other numerical values used in the specification andclaims, are to be understood as being modified in all instances by theterm “about.” Accordingly, unless indicated to the contrary, thenumerical parameters set forth in the written description and claims areapproximations that may vary depending upon the desired propertiessought to be obtained by the present invention. At the very least, andnot as an attempt to limit the application of the doctrine ofequivalents to the scope of the claims, each numerical parameter shouldat least be construed in light of the number of reported significantdigits and by applying ordinary rounding techniques.

It is noted that, as used in this specification and the appended claims,the singular forms “a,” “an,” and “the,” include plural referents unlessexpressly and unequivocally limited to one referent. As used herein, theterm “include” and its grammatical variants are intended to benon-limiting, such that recitation of items in a list is not to theexclusion of other like items that can be substituted or added to thelisted items.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the systems and methods ofthe present disclosure without departing from the scope the presentdisclosure and appended claims. Other embodiments of the disclosure willbe apparent to those skilled in the art from consideration of thespecification and practice of the disclosure disclosed herein. It isintended that the specification and examples be considered as exemplaryonly.

1. A system for activating trapped field magnets in a superconductingmaterial, the system comprising: a superconducting material element; anelectromagnet source disposed proximate the superconducting materialelement; wherein the electromagnet source is configured to produce amagnetic field pulse sufficient to activate the superconducting materialelement, and wherein substantially all of a magnetic field generated bythe magnetic field pulse is directed within an outer peripheral boundaryof the superconducting material element.
 2. system of claim 1, whereinthe superconducting material is a high temperature superconductingmaterial.
 3. The system of claim 2, wherein the high temperaturesuperconducting material is yttrium barium copper oxide.
 4. The systemof claim 1, wherein the superconducting material element is disk shaped.5. The system of claim 4, wherein substantially all of the magneticfield is directed within a diameter smaller than a diameter of the diskof superconducting material.
 6. The system of claim 1, wherein theelectromagnet source comprises a pair of electromagnets, and wherein thesuperconducting material element is disposed between the electromagnets.7. The system of claim 6, wherein the electromagnet comprises awire-wound split field electromagnet with an iron or otherferro-magnetic core.
 8. The system of claim 1, wherein the magneticfield pulse is a single magnetic field pulse.
 9. The system of claim 8,wherein the magnetic field pulse has a duration ranging from about 10milliseconds to more than about 30 milliseconds.
 10. The system of claim8, wherein the single magnetic field pulse fully activates thesuperconducting material element.
 11. The system of claim 1, wherein themagnetic field pulse comprises a plurality of magnetic field pulses. 12.The system of claim 1, wherein the superconducting material element ismaintained within a temperature range sufficient to maintain activationof the superconducting material element.
 13. The system of claim 12,wherein the superconducting material and electromagnetic source aredisposed within a cryostat.
 14. The system of claim 13, wherein thecryostat is a closed system operated at below atmospheric pressure. 15.The system of claim 12, wherein the superconducting material element ismaintained within the temperature range by an evaporated cold gas of alow temperature liquid.
 16. A method for activating a trapped magneticfield in a superconducting material, the method comprising: generatingat least one magnetic field pulse proximate a superconducting materialelement, wherein substantially all of a magnetic field generated by theat least one magnetic field pulse is directed within an outer peripheralboundary of the superconducting material element, and wherein the atleast one magnetic field pulse is sufficient to at least partiallyactivate a trapped magnetic field in the superconducting materialelement.
 17. The method of claim 16, wherein generating the at least onemagnetic field pulse comprises generating the at least one magneticfield pulse with an electromagnet source.
 18. (canceled)
 19. The methodof claim 16, wherein generating the at least one magnetic field pulsecomprises generating a single magnetic field pulse.
 20. The method ofclaim 19, wherein generating the single magnetic field pulse comprisesgenerating the magnetic field pulse for a duration ranging from about 10milliseconds to more than about 30 milliseconds.
 21. The method of claim16, wherein generating the at least one magnetic field pulse comprisesgenerating a plurality of magnetic field pulses.
 22. The method of claim21, wherein a number of plural magnetic field pulses is based on apredicted amount of trapped magnetic field in the superconductingmaterial element.
 23. The method of claim 22, wherein the number ofmagnetic field pulses is based on${B_{T}\left( {r,N} \right)} = {{B_{T}\left( {r,{N = 1}} \right)} \times {\left( {1 + {\sum\limits_{2}^{N}\; {\frac{k}{N}\left\lbrack {1 - \frac{B_{T}\left( {r,I_{EM},{N - 1}} \right)}{B^{*}\left( {r,I_{EM}} \right)}} \right\rbrack}}} \right).}}$24. The method of claim 16, wherein generating the at least one magneticfield pulse fully activates the superconducting material element to atrapped field magnet.
 25. The method of claim 16, further comprisingcooling the superconducting material element to maintain a temperaturesufficient to maintain activation of the superconducting materialelement.